Fault sensing apparatus



J n, 23, 19 2 H. R. SCHULZ FAULT SENSING APPARATUS Filed Dec. 15, 1960COLLISION ZONE TW MOTOR clRculTmf" |NVENTOR l HERMAN R. SCHUL? +V +3V BYm) 3,917,978 FAULT SENSING APPARATUS Herman R. Schulz, Simsbury, Conn.,assiguor to Royal McBee Corporation, Port Chester, N.Y., a corporationof New York Filed Dec. 15, 1960, Ser. No. 76,024 3 Claims. (Cl. 197-17)This invention relates to a fault sensing apparatus employingphotoelectric detectors; more particularly it relates to a fault sensingapparatus employing a photoelectric detector and associated circuitry tomonitor the motions of serially power actuated mechanisms and to respondto delays in the motion of one or more of said mechanisms which persistbeyond a predetermined time interval.

While the present invention finds particular application in thetypewriter or business machine art it is to be understood that there aremany applications involving serially power actuated mechanisms whereinit is desirable to provide monitoring apparatus which responds to delaysin or stoppage of the movement of said mech .anisms which persist beyonda predetermined interval to halt operation and thereby prevent machinedamage.

in the typewriter art, particularly in applications where an electrictypewriter is automatically operated, if a type bar delays too long inthe type guide of the typewriter it is likely to encounter asubsequently actuated type bar causing a pileup.

In accordance with the present invention, actuated type bars, while inthe type guide of a typewriter, intercept a beam of light focused on aphotoelectric cell. The change in photocell current permits theaccumulation of charge on a condenser which, in the event that the typebar remains, in the type guide too long, will charge to an amountsufficient to effect the opening of the typewriter motor circuit therebypreventing machine damage and loss of information. In normal operation,however, where the type bar moves into and out of the type guide in aproper intei al, the beam of light is not interrupted for a sumcientlength of time to enable the condenser to charge to the point where itwill be effective to halt operation; the restoration of the beameffecting a discharge path for the condenser to restore the circuit tonormal.

An object of the invention is to provide a motion monitoring apparatus.

Another object of the invention is in the provision of monitoringapparatus responsive to overlong delays in the motion of a cyclicmechanism,

A further object of the invention is in the provision of a photoelectricmotion monitoring circuit operative in response to overlong delays orstoppage in the cyclic motion of type bars.

A still further object of the invention is in the provision of aphotoelectric motion monitoring circuit operative in response to delaysin type bar motion which persist beyond a predetermined interval forstopping the operation of the typewriter motive source.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings in which like referencenumerals designate like par-ts throughout the figures thereof andwherein:

FEGURE 1 is a fragmentary front view with parts cut away of a typewritershowing a type bar in the type guide of the typewriter and also elementsin accordance with the invention;

States Patent FIGURE 2 is a viewt showing the elements of FIG- URE 1 inside elevation; and

FIGURE 3 is a schematic view of the fault sensing apparatus circuitry inaccordance with the invention.

Referring now to the drawings there is shown in FIG- URES 1 and 2conventional typewriter structure comprising an arcuate type bar segment10, adapted to be moved to upper and lower case positions by linkages(not shown). The type bar segment serves to mount a set of type bars,only one of which is shown at 11 as being pivoted at 12 on the segment10. The segment 10 mounts a type guide 13 which serves also to support aribbon vibrator as is well understood in the art. The type guide has atits upper end two spaced forwardly extending tabs 14 and 15 so formed asto provide a channel which decreases in width toward the typewriterplaten 16 thereby to guide the relatively wide upper and sections 17below the type head 18 of serially power actuated type bars whereby thetype faces strike the platen at the proper place.

For various mechanical reasons not pertinent to the present description,a type bar sometimes is slowed down in its approach to the platen or inreceding from the platen while within the type guide as illustrated inFIG- URE 2. When a typewriter is being automatically operated, actuationof the type bars occurs serially at a predetermined constant andrelatively high rate. If there is any overlong hesitation of the typebar within the type guide then, and this event occurs too frequently tobe tolerated in automatically operated typewriters, a collision betweenthe receding and an approaching type bar will occur in the common pathzone of all the type bars. As a consequence several bars may pile up andmachine damage result.

in accordance with the present invention apparatus for detectingovcrlong hesitation of a type bar within the type guide is operative tohalt machine operation before collision and pileup can occur. Theapparatus comprises as shown in FIGURES l and 2 a photoelectric cell 19suppo1ted closely adjacent the forward end of guide tab 14 by a bracket20 secured to the typewriter cover 21. Associated with the photoelectriccell is a light source 22 supported closely adjacent the forward end ofguide tab 15 by a bracket 23 also secured to top cover 21. The lightgenerated by source 22 is adapted to be focused on the photosensitivearea of the cell. The photoelectric cell is of the photoconductive typecharacterized by a low resistance when exposed to light and. a highresistance when not exposed to light. Hence when a type bar is withinthe type guide the light directed toward the cell is intercepted therebyand the resistance of the cell increases to a high value.

Referring now to FIGURE 3 there is shown a circuit which responds tochanges in photocell current and which energizes a utilization circuitin response to changes which persist beyond a predetermined interval. Asshown in FiGURE 3 the photo conductive cell 19 is connected in serieswith a resistor 24 across supply terminals whereby the voltage at thejunction 25 between cell and resistor will be negative when theresistance of the cell is low and will swing positive when theresistance of the cell increases due to the interception of the lightbeam by a type bar in the type guide. The signal on junction 25 isamplified by p-n-p transistors 26 and 27. More particularly junction 25is connected to the base electrode of transistor 26 which has itsemitter and collector electrode connected respectively to the base andcollector electrodes of transistor 27. The emitter and collectorelectrodes of transistor 27 are connected respectively to ground and tothe negative supply via resistor 28. Transistors 26 and 27 when soconnected comprise an amplifier characterized by a high input impedance,a low outlight directed toward the photocell.

put impedance, and by a high gain. Where the photoconductive cell 19employed has a high signal output and a high signal to noise ratio e.g.a 2N2175 photoconductive cell made by Texas Instrument Corporation,junction 25 may be connected to the base of a single transistoramplifier having its collector and emitter electrodes connectedrespectively to the supply source via resistor 21% and to ground.

The collector of transistor 27 is connected via a resistor 29 to thebase of a transistor 31 which is normally maintained at a positivepotential through connection to a +3 volt source terminal via a resistor32. The collector of transistor 27 is also coupled to ground through acondenser 33. A solenoid 34 is provided in the collector circuit oftransistor 31 and is adapted when energized to open its normally closedcontacts 35 which are connected in the typewriter motor supply linesthereby to stop machine operation.

Normall with the cell 19 exposed to light source 22, transistors 26 and27 are conducting; condenser 33 carries no charge due to the dischargepath provided by conducting transistor 27, and transistor 31 is normallynot conducting. When a type bar 11 intercepts the light beam andjunction 25 goes positive, transistors 26 and 27 will be cut off andcondenser 33 will start to charge through resistor 28. The time constantof resistor and condenser is chosen such that the condenser Will nothave accumulated sufficient charge to render the base of transistor 31negative and conductive, if the type bar which interrupted the lightbeam gets in and out of the type guide in a proper time interval. Inother Words if the object or type bar moves at a rate such that theinterval of light interception is less than the time constant ofresistor 28 and capacitor 33 capacitor 33 cannot charge high enough tocause conduction of the transistor 31. Re-establishing the light onphotocell 19 will rendertransi'stors 26 and 2 7 conductive once againthereby providing a low resistance discharge path for condenser 33. Ifthe type bar hesitates in the guide overlong, condenser 33 willaccumulate sufficient charge to render transistor 31 conductive therebyenergizing solenoid 34; breaking the typewriter motor circuit andhalting typewriter operation.

'In some instances 'tWo or more type bars are simul:

taneously operated resulting in collision and pileup before reaching thetype guide. The same circuit may be employed to detect this type offault by positioning the cell and light source within or at thebeginning of the collision zone shown in FIGURE 2.

While the light source and photocell have been described as being onopposite sides of the path of motion of 'a type bar, it is to beunderstood that the only requirement is that the type bar intercept ordeflect the It should be understood therefore that the foregoingdisclosure relates to only a preferred embodiment of the invention andthat it is intended to cover all changes and modifications of theexample of the invention herein chosen for the purposes of thedisclosure, which do not constitute departures from the spirit and scopeof the invention.

The invention claimed is:

1. In combination with a machine having serially power actuated cyclicmechanisms, apparatus for monitoring the time of passage through apredetermined zone in the path of motion of said mechanisms comprising alight source and a photoconductive cell positioned respectively onopposite sides of the path of motion of said mechanisms, said lightsource being located to direct a beam of light on the photosensitivearea of said cell, circuit means responsive to changes in conductivityof said cell comprising, a condenser for accumulating energy over theinterval said beam is blocked by said mechanisms, and means operative inresponse to a predetermined energy level stored by said condenser forpreventing actuation of subsequent mechanisms.

2. In combination with a typewriter having a plurality of type barsadapted to be power driven through a printing cycle, apparatus formonitoring the time of passage through a predetermined zone in the pathor" motion of said type bars comprising a light source and aphotoconductive cell respectively positioned on opposite sides of thepath of .type bar motion, said light source being j 1 located to directlight on the photosensitive area of said I cell, a condenser, adischarge path for said condenser, 1 means responsive to the blocking ofsaid light on said 1 cell by a type bar for interrupting said discharge?path and for providing a charge path for said COIlfiEIlSSI, meansoperative in response to the charge on said condenser When the intervalover which said light is blocked exceeds the time constant of saidcharge path, and means responsive to the operation of said lastnamedr'rneans for preventing operation of subsequent type bars. I

3. In combination with a machine having a plurality of cyclic mechanismsadapted to be serially power operated, apparatus for monitoring the tim;of passage through a predetermined zone in the path of motion ofReferences Cited in the file of this patent UNITED STATES PATENTS PageSept. 13, 1938 Penther Feb. 24, 1942 Ford Oct. 29, 1957

